First, don't start the engine if there's no oil! Oops .. too late! You might be okay but I'm thinking if there really wasn't any oil ... you'll have to replace something. Not sure what, rings maybe, but something.

What color is the smoke coming out of the tail pipe? Is it blue, white, black? I assume its blue since you said oil is in the tailpipe. I'm suspecting the oil separator. I guess you have oil inside your engine now and need to have it cleaned out. Might try a search as I think others have had to do that before.

Did you check what kind of condition your separator, hoses, valve cover gaskets, etc are in now? I assume you had it replaced before and not changing it now. If you just replaced it now - what kind of condition was the old separator?

I'm sorry I don't have more useful ideas but hopefully people with more knowledge/experience will post soon.